Abstract
This paper presents an integrated experimental and numerical investigation of pre-twisted steel box-section beam-columns. In the experimental study, a series of test specimens were designed to explore the effects of pre-twisted angle ratios (ϕ), loading eccentricities (e), and their directions on the structural behavior. The values of 3°/m and 15°/m for ϕ were considered in the tests. A nonlinear finite element (FE) model, accounting for geometric imperfections, was developed and validated using the experimental results. This model was then employed for a parametric study to investigate the effects of key design parameters, such as ϕ, e, box-section shape (h/b), and effective beam-column lengths (Leff), on the structural behavior of pre-twisted box-section beam-columns. The results show that increasing ϕ shifts the damage pattern from in-plane flexural instability to flexural-torsional instability. For beam-columns subjected to eccentric loading relative to the minor axis of the box-section, ϕ significantly affects the load capacity of members with Leff > 1.0 m, improving their stability. Conversely, for beam-columns subjected to eccentric loading relative to the strong axis of the box-section, the effect of ϕ on load capacity reduction becomes more pronounced for members with larger Leff, i.e., slender beam-columns. For both short and slender pre-twisted beam-columns, the influence of ϕ on load capacity diminishes as the section aspect ratio (h/b) decreases. These findings provide design recommendations for the effective use of pre-twisted steel box-section beam-columns in engineering applications.
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